Industrial seed oils are high in PUFA. If PUFA is easily oxidized, how do they have high smoke points? What am I misunderstanding?
asked byMike_T_1 (9402)
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on July 01, 2012
at 04:07 AM
It's not the triglycerides that are necessarily unstable. It's whatever else is in the oil. Take olive oil as an example. The smoke point increases as you further refine it. You're removing the other things, such as phytochemicals, that are very easily oxidized/burned.
on July 01, 2012
at 02:49 AM
Smoke point and oxidation are unrelated. They easily oxidize, and that's because of the double bonds that are easy to radicalize to make room for the oxygen. Smoking has more to deal with their physical properties, they pack together better and are less likely to smoke.
That still doesn't make them safe to cook with because they've oxidized long before smoking. So just stick with saturated fats when you're cooking with any reasonably high temperature. Saturated fats are nearly impossible to oxidize.
edits to answer comments below:
I'm not sure what determines the smoke point. However, I think that most oils would be all free fatty acids, that's what processing and making the oil would do. It would break it out of the triglyceride. Not sure though, it's not something I've ever read about.
Regarding the ease of oxidation: chemistry doesn't happen at "thresholds". That is, there is no magic temperature at which everything oxidizes, above that temperature it's all oxidized and below that temperature nothing is oxidized. It doesn't work that way. All reactions have "rates" or "how fast they occur". Some reactions happen slowly (metal rusting), some happen fast (an explosion is just a really really fast reaction). Generally, reactions will speed up with temperature, and it's not linear. As a rule-of-thumb, you can say that every 10 degrees you raise the temperature, the reaction doubles in speed. That's why you cook food the heat speeds up the cooking reactions. Back to fats and oils: The rate at which they oxidize is determined by how many double bonds there are. The more double bonds, the more quickly they oxidize. So when you heat an easily oxidized fat, it oxidizes even faster. But you could take a slowly oxidizing fat and heat the hell out of it and make it oxidize fast too. It's all about rates, not thresholds. I'm sure there are tons of tables out there listing the temperature-dependent reaction rates of oxidation for a bunch of fats, I just don't know where to look.
on July 02, 2012
at 07:10 PM
Many have heat-stable antioxidants. Some, like olive oil, do not.
on November 25, 2012
at 05:16 PM
So does this mean that smoking point is unrelated to PUFA-content of the fat, and that refining eg. coconut oil and therefore increasing its smoking point wouldn't make it healthier?
I guess lauric acid or whatever the fatty acids in coconut oil would withstand heat very well but that trace minerals and stuff in unrefined coconut oil would make it smoke at a lower temperature? or is something else removed in the refining of the coconut oil